High-frequency apparatus



June l 1954 c. M. VERQNDA 2,680,209

HIGH-FREQUENCY APPARATUS v Filed May l2, 1950 2 Sheets-Sheet 1 INVETOR CAROL VERO/VDA ATTORNEY June l, 1954 c. M. vERoNDA HIGH-FREQUENCY APPARATUS 2 Sheets-Sheet 2 Filed May l2, 1950 PULSE GEA/04 6 H 7@ o 0 3 8 3 N i105 m f m Z n 5 T N m w mw VM. T m ,M i a@ 7 9 R 7 a 7 f 9 Z d x ,0, 9 a w Ww w 7 /l Lw d Patented June l, 1954 UNITED STATES sai-ENT osi-ICE HIGH-FREQUENCY. Armenians.. Carol'M- Veronda, Island Trees, N, Y assisnr t0.

The SperryCorporation, afcorpor'atin ofiD'ela'- Aware ApplicationMaylZ, 1950, SeriaLNm 161,681:` 12- Claims. (GI. 315-60-` Thisinvention relates to. electron discharge for maintainingan electronv` beam in a suitable devices and, more particularly. to suchdevices configuration is described'in copending applicahavinga novelelectron beam focusing arrangetion XSerial No. 117,187 entitled High Frequency ment... Apparatuain th'ename of Charles E. Rich; iiled For certaintypes of electron tubes it is de- .i September 2217949.r

Sirable to provide an electron beamwith a small An electron discharge device including, among diameter. However, where the electron. beam other thin gsspa,ce charge focusing is provided density involved isnotlargaitisnot very. diiiby the present application. With regardV to cult to` accomplish` thisresult, ysuch asin the space. charge focusing, an electron beam, genaseof acathodev ray tube. or eleotronrnicroi erally speaking, may be permitted to follow a scene,v in. which the-mutual repulsion forces of trajectory. determinedby the initial angle. ofthe electronsare negligible.. Theelectron opticsemelectron gun and by the mutual space charge ployed in such.' electron` discharge devices are repulsion OIQCS 0f' the eltlOnS Under Such based, on a consideration.. of the trajectories of circumstances. the beamconverges to a. minimum individualelectrons without taking into account. 15 and, then .diverges soi thatv the beam` does not thetpresenpf, @there e1 em; 1-ms havev a uniform cross-sectional area over its Toprovide a high power elect'rendischarge length. The electron beamprovid'ed' by thisar.- device, such as a klystron suitable for translrangement hasa substantially apically conjugate mitter typev applications-.itis advisable, to` emconoidal conguration and; Whilev useful for the ploy a-` high. density electron beam.. By. providgeneration of continuous waves, isparticularly ing a klystron transmitter for pulsed applica- Suitable for usev in conjunction with a velocity Vtim-1s it is-.possible to operateV with properly conmodulation devicentended for nulsedoperation trolledfrequency stability. and havinggridded" interaction resonator gaps.

Whereemployingahigh densityelectronbeam `In CertainapplicationsWhere Space considerin. klystron; tubes. the problem. of maintaining ations are. important' itV is. desirable to employ such. a high density. beam in focusduring its a' velocity modulation device operating with a transit througnthe velocity. modulation system high density electron. beam without resorting is present. Three...diiierent typescf beamfocustothe' ifv'rieetie foiSingr-nfeans. An elecingmay be notedVincluding ion focusing, magtron 'dl'scharge device employing space charge neticfocusing and space. chargefocusing. -fOCuSIIIgYl'S particularly Suitable fl $11011 applica!- With regard toY ion foeusing, where residual tions. By employing; a. high density space gasmeleeuies are present within thev vacuum ,chareedioeused electron beam it is' possible t0 envelope off the tube structure, such ions. are obtain. high. power .output pulses of' desirable eifectivevfor neutralizing the space charge of COrlguiationwitha compact electron discharge the electrons. of. the beam, thereby permitting asstruiure. In addition yvith cascade bunching the beam to traverse the length of the tube with- 0f eleCtIOIlS an leCrOIl dlscharge deVlCe may be out undergoing excessive defocuslng owing to' the Operated With a relatively low drive power mutuaI repulsion kofelectrons.. Generally speak- Accordingly; itlisan'ob'iectof the present ining, ioniocusingfis limited to electron. discharge venticn to.. provide a space. charge focusing devicesoperatedascontinuous Wave generators 40 meansfor'obtainmg. an' electron beam having a in view of the factthatthere yare no. ionspresent substantially apically conjugate conoidal conat thebeginningofa pulse to form asuitable figuration.

.electron beam configuration..v .Consequently,. a Aiurther, object lies. inthe. provision. of an pulse generator tube employing, ion focusing may improved velocity modulation device suitablefor provide-ahighpower output.pulsehavingsides supplying. `steep sided radiov frequency output or. edges whicharanotsuni'ciently steep. for vcerpulses..

tainapplications, A. still further` object. iste-provide a. velocity Magnetic focusing. may be. provided' by an modulationelectron, dischargedevice. of acomaxially-directed.4 magnetic field; whichiseiecpactv configuration. y

tive for. maintaining ar high density electron 50 An additionlobject isftoproyide.an'improved beamunifor-m .inA Gross-sectionab area i011 any electron discharge/Germans .generaties pulses desired distance. Such magnetic focusing; is hav-ing azrela 'velyglarge-magnituderof power.. :neel-5.111:foe-velocity*modulationfdewces operated Y bothas. continuous. waves and: radio frequency tron havingzelectrostaticand spacefharge focuspulsezgeneratora The userofiimagneticr'focusinm 555' ing. means:

' cludes ,ported by sleeve I4,

noted that the diameter of focusing electrode Afiled March 15, 1949, now

`ternal potential source,

Another object is to provide an improved electron collector.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings, wherein the invention is embodied in concrete form.

Fig. 1 is a longitudinal View, mainly in cross section, of an electron discharge device according to the present invention.

Fig. 2 is a fragmentary cross-sectional view of an alternate embodiment of an electron collector, which may be employed with the electron discharge device of Fig. 1.

Fig. 3 is a view, mainly in cross along lines 3-3 of Fig. 2.

Fig. 4 is a view showing, among other things, a grid structure taken along lines 4-4 of Fig. 1.

Fig. 5 is a view showing, among other things, a grid structure taken along lines 5--5 of Fig. l.

Fig. 6 is an enlarged View, mainly in cross section, showing the structure of the cathode ofv section, taken Fig. 1.

all of the above figures to indicate corresponding parts.

Referring to Fig. l aligned dinal axis II of an electron an electron beam producing means, which ina means for supplying electrons, such as cathode button or electron emitter I2, the upper surface of which is suitably oxide coated and subalong the longitu- 'stantially spherically concave in cross section about the longitudinal axis II. The edge of the aperture of the apertured cup I3, which is supprovides a first line conductor or edge i6 positioned outwardly of and along the longitudinal axis II in a direction away from the cathode button I2. Accordingly, it will be the aperture of cup I3 is larger than the diameter of the cathode button I2.

The end of the sleeve I4 in a direction toward the main body of the electron discharge device pro-vides a second line conductor or edge I'I, with the second edge I'I being located outwardly of the cathode button I2 to a greater extent than the first edge I6. The second edge I'I is, in addition, disposed along the longitudinal axis II in a direction away from the cathode button I2 to a greater extent than the first edge I6. The first and second line conductors or edges I6, I1 constitute an electrostatic iield forming means or I8, which is ing to the principles disclosed in copending application Serial No. 81,480 entitled High Frequency Apparatus in the name of Chao Wang,

Patent 2,564,743.

For accelerating and directing electrons emanating from the cathode button I2 toward the main body of the electron discharge device. an accelerating electrode or anode I9 is provided, which anode I9 is suitably energized by an exas discussed hereinbelow. Under the influence of the focusing electrode I8 and the anode I9, a high density electron beam is formed, in which the individual electrons thereof traverse substantially rectilinear trajectories and travel toward a point.

Three separate and distinct electromagnetic field defining means are positioned to receive or discharge device isY designed accordpassing therethrough.

to be traversed by this high density beam successively in energy-exchanging relation. The electromagnetic field defining means may include cavity resonators 2 I, 22 and 23, each being provided with an electron-permeable region or gap 24, 26 and 21, respectively, through which the high density beam passes. The wall of resonator 2i which faces the cathode button I2 provides the previously identified accelerating electrode or anode I9.

Between the rst two resonators 2I, 22 there is provided a means defining a drift space, such as drift tube 28. Similarly, between the second and third resonators 22, 23, there is provided a means defining a further drift space, such as drift tube 29. It will be noted that the end ones of the resonators 2I, 23 are provided with singly-reentrant configurations.

The walls of the drift tubes 28, 29 are tapered inwardly toward the gap 26 of the intermediate resonator 22, so that the drift tubes 23, 29 have a minimum cross-sectional area in the vicinity of the gap 26. It will be noted that the walls of the drift tubes 28, 29 are provided with an appreciable thickness, which permits heat developed internally of the electron discharge device to be more readily conducted to the exterior thereof. To the same end, the walls of the drift tubes 23, 29 are preferably formed of a material having a relatively high thermal conductivity, such as copper. The configuration of the internal walls of the drift tubes 28, 29 is such as to substantially follow, while being somewhat spaced from, the envelope of the electron beam The internal Walls of the resonators 2I-23 are preferably constituted of highly conductive material to achieve efficient electrical operation. This may be accomplished by forming these parts 2I-23 of copper, silver, of a material plated with such metallic substances.

In view of the fact that resonator 2l is effective for impressing velocity Variations upon the electron beam traversing the gap 2A thereof, this resonator 2I may more generally be termed a rst means for velocity modulating the electron beam. To suitably excite resonator 2I, which resonator 2I may also be termed an input or buncher resonator 2i, a means for coupling electromagnetic energy thereto, such as an input coaxial transmission line terminal post 3|, is provided. The intermediate resonator 22 is effective for further impressing velocity variations upon the electron beam traversing its gap 26 and hence may more generally be termed a second means for velocity modulating the beam. It will be noted that no provision is made for coupling electromagnetic energy to or exciting the intermediate resonator 22, the necessary excitation being provided by the electron beam traversing the gap 26 thereof.

Resonator 23 is effective for extracting electromagnetic energy from the electron beam traversing its gap 2'I and, consequently, may more generally be termed a means for extracting electromagnetic energy. At times such a resonator 23 is referred to as an output or catcher resonator 23. To deliver electromagnetic energy from the output resonator 23 to a load (not shown) a means for coupling electromagnetic energy, such as output coaxial line terminal post 32, is provided.

In order to provide for the adjustment of the resonant frequency or tuning of the resonators 2 I-23, they are formed with flexible diaphragme r-end Walls 332 34 and135 respectively. Lugs 30'. are-rigidly mounted on thev exterior walls.- of the-resonators 2 |231- and =angelike membersY 3 6; 40'- are rigidly. secured to the` drift tubesv 28, 29, respectively. rIlhe lugs` 30 and flange-like members` 36, 40. are suitably apertured to. accommodate longitudinally-extending tuning screws 31, 38, with nuts.39 cooperatingwithithe tuningr screws 3'?, 38'; to regulate the axiall separation of the lugsfandflangedikemembers 36, 40i The upper endioftunmg screw. 31= and the interinodiate portion oftuning screw 358 are rigidly secureditoithefange-like members 49, 36, respectively, asby soldering.l

BysuchY adjustment` thelresonantfrequency of the resonators 2l-23 may be varied. Withan increase: in'A the axial separationV or longitudinal spacing of a resonator gap, such-as, for instance'. gap Z4', the frequency ier-increased;A The`l tuning is. accomplished by opening4 one. of the` nuts: 39 andi tighteningl one ofl the opposing nuts 39' in the desired direction. Similarly, the` resonant frequencyA is decreased as the axial separation` of a; gap, suchasr gap 24, isreduoed Y If desired; thermal compensation for` var-iations inA ambient. temperature may be employed. Such. ambient.v temperature variations alter the volumesof theresonators 2-I-23; thereby introducing changes inthe resonantfrequencies thereof.: By. suitably selectingA the tuning screwsr3'l,

linear coeiiicient of vided for dissipatingv Such-heat; .suchras-A cooling ns 46, supportedby rodsifll. Morepspecically, :four symmetrically VdisposedV rodsi4lfaresupportcd by platefl and have helicallyshaped cooling the metallicblock 4|is also joined tolsieever, 56:.through vthe vitreous tubular member 51, with sleeve 53` being additionally connected: to plate 52; Alliof the aforementioned connectionsv areV eiectedl in a vacuum-tight manner in order: to-- insure the preservation of the internal vacuum-of; the elec-,-

tubes 28, thel wall portions -ofi the Aresonators 2 l-23, are :of a vacuum-tightfconstruction..

be provided grids 6|, 62;,63, 64; and66; El; respeively.v Theelectrical diameter of. the gaps jor apertures 24, 2621 of the resonators-2i-23, respectively, by'virtue of' the presenceofgrds ith-6I', 66, 6ft maybezlargerthaniwouldiotherwise be the case without loss of efficiency resulting` fromunevennessoftbunching across .the-diameter ofthe electron beam;y

Although not essential, it is preferable toform the exity gridv 3l of the: output: resonator of a larger diameter, ascompared; for instance, with the entrancegrid. 6,61' thereof; Thus,l thev possibili-` ity of. interception 1 of th'effbunchied electronbeam by: the z walls of.t the output. resonatorv Krissmini'.- mized.. Itvvilly bel noted: that the gap or: aperture 2:1: is' form-edf with=a ttapered:congurationf ever, it is believedithat nmisunderstandingwil occur; by describing, for instance; the er1-drones of the resonators 2 l, 23l as; having larger apertures 24, 21 than the aperture 26 of thezintermedla'te resonator 2.2;

In operation, electrons emanatingfromlxthe cathode buttonA l2:l are. accelerated vtovvarclftiie anode I 3;.when1adiiference of eIectrcalpOtentil is` impressed therebetween, as discussed more fully hereinbelow` inlconnectionwith Fig: 7. ing-'the transit tof electrons toward'. tlief anodei44 t! the' eld forming means .or focusing electrode1 I8', whichis constitutedofz first' and .secondi line conelectron bea-m is designed to simulate a spherical flow of electrons. Accordingly, along the-beam boundary` in the region between the cathode-but;

Stated' focusing. electrode |8; the presence` of complete space charge; a zero voltage gradient normal to=the-edge-'ror'boundary of theelectron beam.

Thehigh density electron beam'- after? passing the anode !9 traverses in successionthegapseZ, wand Zlfofv the resonators. 2l-23; respectively. Gwingto .the presence of anV electromagnetic-l-eld inA the input' resonator 2 l whichv resonator' 2li* is excitedby means ofi high frequency energy suppliedl thereto through coaxial i line terminal? post 23A such density modulated beam' isu effective for exciting the output resonator 23,. Electromagnetic energy maybe COlllJledfrom theVY Qllpllt .resonator 2`3to aload (not shown)I by. meansof the output coaxial transmission line terminal post 32.

After passing the gap 21 the spent electrons are collected on the conical surface 42 of the metallic block 4|.

. With such cascade bunching, it will be noted that the first two resonators 2i, 22 are both effective for providing velocity modulation of the electron beam. The intermediate resonator 22 is excited into oscillation solely through the interaction of the electron beam therewith, with no electromagnetic energy being introduced therein from an external source. Resonators 2l, 22 may be said to operate as a voltage amplifier and resonators 22, 23 may be said to operate as a power amplifier.

In the case of three resonator klystrons operatedr as an oscillator-buffer tube a small drift space between the second and third resonators is employed to prevent overbunching, inasmuch as .the electrons are satisfactorily bunched at the second gap of an oscillator and additional bunching is undesirable. In the case of a three resonator tube, such as the electron discharge device of Fig. 1, additional bunching is desirable to achieve suitable amplification, thereby permit- ,ting the operation of the device with a relatively 4small magnitude of drive power. The bunching lat the gap 26 will not be complete, but the additional bunching occurring in the drift tube 29 vwill result in optimum bunching at the gap 2T of 'the' output resonator 23. In the event that maximum gain is desired, the axial lengths of the drift tubes 28, 29 are made substantially equal.

With such cascade bunching it is preferable that the intermediate resonator 22 be provided with a relatively large magnitude of shunt resistance. Under such circumstances the resultant small current variation in the electron beam during its interaction with resonator 22 `will be effective for developing a relatively large radio frequency voltage across the gap 2E. Where it is possible to develop a suiciently large magnitude of voltage across the gap 26 of the -intermediate resonator 22 by means of a relatively law current variation in the electron beam, a corresponding relatively low magnitude or drive voltage is required.

In order to achieve substantial bandwidth, which is an important consideration in the production of steep-sided or steep-edged pulses, it has been found advisable to design the intermediate resonator 22 with a relatively low Q, lwhich may be defined as follows:

.Where R511 is the shunt resistance, w is the angujlar operating frequency, L is the inductance and C is the capacitance. It is the Q of the intermediate resonator 22 which is important for determining the overall Q of the electron discharge device. It is apparent that the Q of the inter- `mediate resonator should have a relatively small 'magnitude in view of the following relationship:

i Buf12 (2) there Bw is the bandwidth, and f is the opel-ating frequency.

, From Equation 2 it is apparent that the bandwidth may be increased for a given operating 'frequency by employing a smaller magnitude of From a consideration of Equation 1 it appears that the Q may be reduced by employing a smaller magnitude of capacitance. To this end, the diameter of the gap 26 of the intermediate resonator 22 is made smaller than the diameter of the gaps 24, 21 of resonators 2|, 23, respectively. Stated somewhat differently, the diameter of the gaps 24, 21 of the end ones of the resonators 2l, 23 is larger than the diameter of the gap 26 of the intermediate resonator 22. By reducing the Q of a resonator, such as intermediate resonator 22, it is apparent from a consideration of Equation l that the shunt resistance will correspondingly be reduced in view of the fact that these quantities are directly proportional.

As pointed out previously, in order to achieve the effective cascade bunching it is advisable that the intermediate resonator 22 be provided with a relatively large magnitude of shunt resistance. However, it has been found possible to reduce the magnitude of the capacitance of the intermediate resonator 22 and at the same time obtain a sufficiently high magnitude of shunt resistance for this resonator 22 to obtain efflcient cascade bunching. In addition, the electron discharge device is provided with an appreciable bandwidth, which permits the generation of steep-sided radio frequency pulses. Such pulses owing to the high density of the electron beam have a considerable magnitude of power.

rThe shunt resistance of a resonator, such as intermediate resonator 22, is constituted of transit time electron loading, slow secondary electron loading and radio frequency circuit losses. With regard to transit time electron loading, electrons require a finite time to traverse a resonator gap, such as gap 26 and, consequently, load the resonator 22. It is possible to reduce transit time electron loading by decreasing the gap transit angle.

With regard to slow secondary electron loading, primary electrons impinging upon the grid structures, such as grids 63, 64, cause the emission of secondary electrons. With the emission of such secondary electrons having substantially zero velocity, there is present in the radio frequency field of the resonator gap, such as gap 26, spurious or secondary electrons during several cycles of the radio frequency energy. Such spurious electrons leave the gap 26 in random phase, thereby extracting energy from the electromagnetic field. Such loading is proportional to the current intercepted at the resonator grids, such as grids 63, S4, and to the secondary emission coefficient of the grid material. This loading is also inversely proportional to the square of the gap transit angle for the beam electrons. Accordingly, it appears that by increasing the gap transit angle, secondary electron loading may be reduced.

With regard to the radio frequency circuit losses of the resonator 22, such losses are inversely proportional to the spacing of the gap 26, while the coecient of coupling between the radio frequency field at the gap 26 and the electron beam passing therethrough decreases as the gap spacing is increased. Consequently, in order to provide a suitable resonator, such as resonator 22, it is essential to select its dimensions in view of all of the foregoing considerations.

While, generally speaking, all of the resonators 2 I-23 are tuned to the same resonant frequency, it is possible to increase the power output of the electron discharge device by detuning the second `or intermediate 4'resonator 2.2 2 'slightly `to the .high .frequency side of the resonant fre- .quency .of the input and output resonators 2l, 23:'and by increasingat the'same time the magnitude ofthe .drive powersupplied to the input resonatorzZI through its associated terminalpost 13| an electron which has traversed the gap 24 at a time when the radio frequency eld in the input resonator 2I was :1ero and increasingmay be Vsubjected to more effective further velocity modulation by traversingthe gap 2S of the intermediate resonator L22 ata time when 'the radio frequency eld'in the intermediate resonator 22 .of the output resonator -23 results. In thismanner the most effective cascade bunching occurswith maximum power developed in the output resonator 23.

'In order to achieve an output power in excess of that which Wouldoccur, for instance, by use In this couple the resonators 2l, 22 andresonators V22, 5'"

23, respectively, provided vwith oppositely tapered configurations.

By virtue lof the high density velectron .beam :of the aforementioned conoidal shape, .a .large magnitude of outputpower is developed in the catcher resonator A23with an Aelectron discharge structure which is axially or longitudinally compact. In addition, `there is no necessity for the provision of yany structure. In 4density beam prior to its action with the gap 24 of the input resonator 25, electrostatic eld forming means, such as focusing electrode I8, are provided. To maintain the electron beam "throughout- `its including resonators 'ZI-"23, fonmaintainingthe electron beam in a substanedge of the electron beam Whereitzis advisable to .discuss vjointly the action of the focusing electrode I8 and the. space charge focusing means, which may include, for instance, the converging configuration of the drift tubes 28, 29, it is convenient'to regard the focusing electrode I 8 as being effectiveforforming a high density electron beam and the .space charge focusing means as being eifective for maintaining the electron beam in a .substantially conoidal configuration.

It is frequently convenient to speak of the size of the .electron-permeable :regions or .apertures 24, 2E and 2l of the resonators 2I-23, respectively. Such apertures 24, 26 andJZTextendlongitudinally through the resonators 2I23 along the longitudinal axis I I of the device of Fig. 1. It will be noted that 7the size of such apertures .24, 26 and El' may be defined in terms ofthe cross-sectional area of their `sections taken at right angles tothe longitudinal axis II.

and cooperating with the remainder of the structureof the device of Fig. l, it will be understood that other electron beam V'forming yarrangements .might be employed. For instance, if desired, a

focusing electrode constituted of a surface of complex conguration, and suitable for providings-a zero voltage gradient perpendicular to the might be employed. While vthe electron discharge device of Fig. i1 has .been shown as constituted substantially of a gure-of-revolution about the longitudinal parallel to the axis IVI yand positioned exterior rof thev cross-sectional'structurefofFig. i1. vMoreover, the longitudinal cross-sectional view of Fig. 1 might be regarded substantially as a figure-oftranslation, in which case an elongated 'striptype cathode could be employed together with a focusing electrode, such as described in the aforementioned application VSerial 'No. 81,480.

. Referring to `Figs. .-2 and 3, fan alternate vembodiment for the electron vcollecting means, including the block 4I, lof 'the -device of Fig. 1 is shown. A metallic member or block '58 yis provided with means, including the end portion 59 Vof the block T58, vfor collecting electrons of an electron beam having a substantially Vapically conjugate conoidal yconfiguration. More specifically, the end .portion "59 of the block 58, which portion 59 faces thecathode button I2, 'is provided with a'toothed configuration in cross `section. Each tooth member '66, with the exception ofthe central one, is formed with a righttriaifigular shape, ysuch that the .leg closest to the longitudinal vaxis I I .extends parallel thereto.

The-arrangement of the portioni? is particularly suitable for :collecting spent electrons of a beam of the aforementioned lconoidal configuration without permittingspurious electrons, such as those arisingfrom secondary emission, 'from` traversingthegap 2.7 vof theoutput resonator 23. Such spurious electrons :will fact to impair :the

. 1l operating characteristics o the electron discharge device.

Referring to Fig. 4, an enlarged cross-sectional view of exit grid 62 of the input resonator 2| is shown. Grid 62 is formed with a plurality of V-shaped members or vanes 66 and a plurality of J-shaped members or vanes 68, with each of the V-shaped members 68 substantially surrounding a J-shaped member 68. A J-shaped member 69 is additionally positioned between the V-shaped members 63.

Both the V-shaped members 68 and the J- shaped members 69 are preferably formed of a ribbon-type material to provide a vane-type structure with the wider dimension extending parallel to the longitudinal axis In addition, the V-shaped members 88 are preferably formed of a metallic ribbon which is thinner than the ribbon employed for the J-shaped members 69 so that fewer electrons are intercepted thereby. f

At the same time it is advisable to provide a more rigid type construction for these members 68 in View of the fact that they extend for a greater distance than the .l-shaped members 68. This is accomplished by the V-shaped construction in that the two leg portions of the members 63 are continuous in the region of the center of the grid 62. In connection with the J-shaped members 66, it has been found preferable to employ the J-shaped configuration as contrasted, for instance, with a J-shaped conguration so that a minimum electron beam interception area is presented to the electron beam. This is particularly important in view of the fact that the electrons in the outer region of the grid 62 are traveling in paths which are less parallel with respect to the longitudinal axis than electrons in the central region of the grid 62. Consequently, such outer region electrons would be presented with a larger intercepting area in the event that a grid element, such as members 69, was formed with a V-shaped configuration.

Dimensions for the members 68, 69 may be as follows: member 68, 68 may be formed of ribbons having thicknesses of 0.003 and 0.005 inch, respectively, while both members 68, 69 may be formed of ribbons having widths of .062 inch. Such dimensions, it will be understood, are merely illustrative and are not to be construed in a limiting sense.

The entrance grids 8|, 66 of resonators 2|, 23, respectively, may have the same construction as grid 62 of resonator 2|. The exit grid 61 of the catcher resonator 23 may be formed with the same general configuration as that of grid 62, but it will be noted that grid 61 is of larger diameter.

Referring to Fig. 5, an enlarged view of the exit grid 64 of resonator 22 is shown. Grid 64 is constituted of a plurality of J-shaped members or vanes 1|. The J-shaped construction for the members 1| provides a minimum of electron beam intercepting area in the central region of the grid 64. The entrance grid 63 of the intermediate resonator 22 is similarly formed.

Referring to Fig. 6, an enlarged view of the cathode structure of the electron discharge device of Fig. l is shown. gization of the electron emitter I2, there is positioned therebeneath a heater 12, which may preferably be formed of tungsten wire. Electrical energy may be coupled to the heater 12 by means of input leads 13, 14, which galvanically contact the ends of the heater 12 through leads 16, 11,

For the thermal ener-- which may be formed preferably of molybdenum. The upper portions 18, 19 of the input leads 13, 14, respectively, may be formed preferably of copper while the lower portions 8|, 82, respectively, may be constituted preferably of nickel.

While for purposes of electrical conduction, copper is a particularly suitable material, it is also an excellent thermal conductor. Accordingly, to prevent the excessive dissipation of heat endwise of the electron discharge device, it has been found preferable to employ a less highly thermal conducting material for the lower portions 8 82 of the input leads 13, 14, respectively. It will be understood that the input leads 13, 14 may be formed of a single material, such as copper, nickel or other suitable electrically conducting material.

In order to direct toward the cathode button |2 and prevent the escape in the direction of the input leads 13, 14, the heat developed by the heater 12, heat shields 83 are positioned therebeneath and supported by a heat shield supporting rod 84, which in turn is rigidly secured to the platform 86. The upper portions 18, 18 of the input leads 13, 14, respectively, are also positioned and supported by the platform 86, with an insulative member |25 together with its associated clamp |30 interposed between upper portion 19 of the input lead 14 and the platform 86. The cathode button I2 is supported by the platform 86 by means of a cylindrically-shaped cathode supporting member 81, which is provided with a flange portion 88, `Screws 83 positioned in suitably cooperating apertures in the platform 86 and the flange portion 88 are effective for accomplishing the desired result. The upper end of the cathode supporting member 81 is rigidly secured to the lower surface of the cathode button |2, as by welding.

Additional heat shields 9|, 82, positioned substantially coaxially with respect to the longitudinal axis I I, are spaced from one another and sleeve |4 and, in addition, supported by struts 93, 84.

Sleeve |4 is fastened to an apertured disc 96 by means of screws 31. A tube 98 is provided with a shoulder 98 to suitably position and support insulating member l0 which in turn serves to position and additionally support the input leads 13, 14. Plate 49 is connected to the end plate |02 by means of sleeves |03, |04, which sleeves |03, |04 are interconnected by a tubularly shaped insulating member |06. In View of the fact that the parts 49, |02|04 and |06 define a portion of the vacuum envelope of the electron discharge device, the interconnections thereof are formed in a vacuum tight manner.

The tube 98 is also supported by end plate |02. Sections of the lower portions 8|, 82 of the input leads 13, 14 are surrounded by tubular members |01, |08 which are interconnected by means of vitreous insulating members |09, in a vacuumtight manner. Rings I|| are provided at the lower end of the tubular portions |08. The connections between the end plate |02, the tubular members |01, the insulating members |08, the tubular members |00, rings |I| and the respective input leads 13, 14, similarly provide vacuumtight joints. The operation of the device of Fig. 6 will be discussed hereinbelow in connection with the operation of the circuit of Fig. '7.

Referring to Fig. 7, there is shown the cathode button |2' and the heater 12 in schematic form, with these parts joined together electrically as shown in Fig. 6 where the cathode button |2 is 13 connectedf to'ztlfieinputf lead lthrougl'i theic'atfrode supporting member.` 87:' and the platform 86. Ai lila-ment transformer: I fl 2T is arran'gedz` with'. its

atl ground potential: A bypassing: condenser- |23 isshunted across the=indicatingrmeter 22,1'

During operation, `theelectrical' energy for supplying theA heaterY '|23 mty:A be continuously de:- l-iveredthereto through the-transformersv H2 and |211. Suitablepul'ses may be impressedfuponvthe cathode I2`by-'meansofthe pulse generatorf ISIS and the pulsing transformer IIB.. In View of the fact that the main body of the device',v including the resonators 2-|-23, and, more particularly; the anode or acceleratingr electrode Y I 91 are preferably maintained at ground. potential; the potential of Athe'-ca1',l`1ode -|2, I2 isfreducedf during such times as 1 an energy interchange between an electronn beam'- and theresonators 2|-2'3 isf desired. Thus; pulsesareintroduced by means 4of having a repetition ratel and stance` the* tubular membery 5|, to arpoint of ground potential thereby maintainingrv tl'ieen*- Velope of the-deviceat groundpotential. Inad'- dition, lead I-Z-Il (Fig: `1)- interconnects the-elec;-

Owing 'tc thefconstruction off the1 cathode;4 asito the focusing-:electrode I8? which isldiierent from that applied to the cathode button l2, I2. A suitable" focusing electrode potential Zmay be-applied to theyendplate-Iil-Z Such'aanzarrangement button 'la-the insulating, member ma; the, m-

1.4 arranged? (Figcy 1')v the: magnitude; of"7 the current.

ternal vacuumof the-electron dischargen dev-ice: Tltlie same-end; sleeve |32 isconnectedi-'tdtlie sideewalls of the resonators 2|, 2'3"' in'- ar Vacuum# tight manner.

trativeandfnotin alimitingsense. K' J While the. device of'Fig.1lis particularly useful forthegenerationof high .povver pulseslvritli suit?- It; is. apparenty thatA many changes. could''be made, mi' theVv construction Y of the device of Fig'.

out depar.ting.,from theV scope thereofl, For' instance, as:discussedhereinabova the. electron col.- lector.: on Fig.V 2,. mightfr be.l employed,V inf thel der ofz'l'ig; 1,.the cathodeeassembly mightalbe moiclied;A and: thesdeviceoperated eltherf asfifa: pulsefonlcontinuoixsewavef generatorg. Acoor'clirlgii ly;itfisintendedzthatallmatter contained ini-the abovefdescriptionl or' shown"v infr. the?. accompanyingVA drawings shall be interpreted? asf illustrative and* notn inL a" limitingfsense:

l'. High. frequency' apparatus" comprising first; second and third` cavityresonators; each" o'fsaid resonators havingwin` electron-permeable gap-Va; irst` drifttube' positioned intermediate said l'ist andn second f resonators; and-` a secon-d* drift`v tube positioned.v intermediata said secondandxithird resonators,k the; inner' Walls' of; said" drift.v tubes beigjtapered" and'c'onver'ging 'towardw thergapj-of s saidlsecondreson'atoi' 2. The high frequency apparatus as defined in claim 1 wherein the lengths of said iirst and second drift tubes are substantially equal.

3. The high frequency apparatus as defined in claim 1 wherein the distance between the midpoint of the electron-permeable gap of said rst cavity resonator and the midpoint of the electron-permeable gap of said second cavity resonator is substantially equal to the distance between the midpoint of the electron-permeable gap of said second cavity resonator and the midpoint of the electron-permeable gap of said third resonator.

4. The high frequency apparatus as dened in claim 1 wherein the cross-sectional area of the electron-permeable gap of said second cavity resonator is less than the cross-sectional area of the electron-permeable gaps of said iirst and third cavity resonators.

5. An electron discharge device comprising means for producing an electron beam, first, second and third cavity resonators, each of said 4resonators having an electron-permeable gap, said gaps being aligned along an axis and positioned for receiving and passing said electron beam in succession, the distance between the electron-permeable gap of said iirst resonator and the electron-permeable gap of said second resonator being substantially equal to the distance between the electron-permeable gap of said second resonator and the electron-permeable gap of said third resonator, the cross-sectional area at right angles with respect to said axis of said gap of said second resonator being smaller than the cross-sectional area at right angles with respect to said axis of said gaps of said first and third resonators.

6. An electron three cavity resonators, each of having an electron-permeable gap,

discharge device comprising said resonators said gaps being substantially aligned along an axis, means including a cathode located along said axis for producing and projecting an electron beam along said axis successively through said gaps in energyexchanging relation with said resonators, said electron beam tional area within said electron-permeable gap of the intermediate one of said resonators and having a larger cross-sectional area within the electron-permeable gaps of the end ones of said resonators, each of said gaps of the said resonators having a larger area at right angles relative to said axis than that of said gap of the intermediate one of said resonators.

7. High frequency for producing an electron beam, a first cavity resonator, a first drift tube, a second cavity resonator, a second drift tube, and a third cavity resonator, all of said foregoing elements being aligned along an axis and located in axial consecution, all of said resonators being provided -with substantially circular apertures for receiving and passing said electron beam, the diameter of said aperture of said second resonator being smaller than the diameters of said apertures of said first and third resonators, the walls of said drift tubes being tapered in the direction of said aperture of said second resonator, whereby a space charge focused electron beam is formed having a substantially apically conjugate conoidal configuration.

, 8. The invention set forth in claim 7, further including a collector electrode ,in the path of said beam beyond said third cavity resonator, said having a diminished cross-secend ones of cross-sectional apparatus comprising means I electrode including a surface facing said resonator and provided with a plurality of substantially concentric and approximately co-planar grooves, said grooves having in cross section a substantially right triangular shape, with the hypotenuse diverging outward from the central axis of the structure in the direction of said beam.

9. In an ultra high frequency velocity modulation device, an electron source, electrostatic field forming means for initially converging the electrons emanating from said source to form a high density beam, the cross-sectional area of said high density beam of electrons converging to a minimum value at a predetermined point along the path of said beam and diverging beyond said predetermined point, and three cavity resonators having electron-permeable portions aligned along the path of said beam to be successively traversed by said high density beam, the electron-permeable portion of the intermediate one of said resonators being situated along the path of said beam at said predetermined point and being of smaller cross-sectional area than the electron-permeable portions of the others of said resonators.

10. An electron discharge device comprising cathode means for producing an electron stream directed along an axis; and iirst, second, and third resonators located successively along said axis and each having an electron-permeable portion aligned with said cathode along said axis; said cathode means including a focusing electrode extending toward said resonators comprising means for causing the electrons of the electron stream to converge to a minimum crosssectional area within the electron-permeable portion of said second resonator, said electron stream diverging along said axis beyond the electronpermeable portion of said second resonator.

11. The apparatus of claim 10, wherein the cross-sectional area of the electron-permeable portion of said second resonator at right angles with respectfto sad axis is smaller than the cross-sectional areas of the electron-permeable portions of said first and third resonators.

12. The apparatus of claim 1l further including a iirst drift tube located intermediate said first and second resonators, and a second drift tube located intermediate said second and third resonators, said drift tubes being tapered and converging toward said second resonator.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,136,610 Colby Nov. 15, 1938 2,316,276 Motz Apr. 13, 1943 2,394,396 Mourmtseff Feb. 5, 1946 2,399,752 McCullough May 7, 1946 2,407,707 Kilgore Sept. 17, 1946 2,413,725 McNally Jan. 7, 1947 2,422,695 McRae June 24, 1947 2,464,349 Samuel Mar. 15, 1949 2,466,704 Harrison Apr. 12, 1949 2,469,843 Pierce May 10, 1949 2,475,652 Varian et al July 12, 1949 2,480,133 Hansen Aug. 30, 1949 2,498,673 Goudet et al. Feb. 28, 1950 2,544,675 Hamilton Mar. 13. 1951 FOREIGN PATENTS Number Country Date 606,801 Great Britain Aug. 20, 1948 

